1. Field of the Invention
The present invention relates to novel peptides which are useful as drugs, such as diuretic agents, therapeutic agents for hypertension, therapeutic agents for heart disease, and muscle-relaxing agents.
2. Description of the Background
Of patients with hypertension, 95% have essential hypertension, and half of these have sodium-sensitive hypertension. It is likely that sodium-sensitive hypertension is regulated as a function of Na-volume in the living body. It has been assumed that in the factors relating to natriuretic action, there is an unknown humoral factor (a third factor) in addition to GFR (glomerular filtration rate) and ardestrone. The third factor involves a substance which inhibits Na-K ATPase and one which does not inhibit it. Therefore, it has been expected that clarification of the third factor would make a significant contribution toward understanding the cause and therapy of essential hypertension.
Since the autumn of 1983, the structure of natriuretic hormone as secreted from an atrium has been established. This hormone is a third-factor substance without Na-K ATPase inhibitory activity. It possesses both strong natriuretic activity and muscle-relaxing activity. One human natriuretic peptide hormone is named .alpha.-human atrial natriuretic peptide, which is abbreviated as .alpha.-hANP, having the following structural formula: ##STR2##
One rat natriuretic peptide hormone is named .alpha.-rat atrial natriuretic peptide, which is abbreviated as .alpha.-rANP, having the following structural formula: ##STR3##